Imagine that the balloon is actually completely flat and (to all intents and purposes) stretches infinitely in X and Y directions without wrapping around. As I

Imagine that the balloon is actually completely flat and (to all intents and purposes) stretches infinitely in X and Y directions without wrapping around. As I understand it, we currently believe we're in a 3D version of that: https://en.wikipedia.org/wiki/Shape_of_the_universe https://en.wikipedia.org/wiki/Shape_of_the_universe